function getScrollTop() {
    var scrollTop = 0, bodyScrollTop = 0, documentScrollTop = 0;
    if (document.body) {
        bodyScrollTop = document.body.scrollTop;
    }
    if (document.documentElement) {
        documentScrollTop = document.documentElement.scrollTop;
    }
    scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop;
    return scrollTop;
}

//文档的总高度
function getScrollHeight() {
    var scrollHeight = 0, bodyScrollHeight = 0, documentScrollHeight = 0;
    if (document.body) {
        bodyScrollHeight = document.body.scrollHeight;
    }
    if (document.documentElement) {
        documentScrollHeight = document.documentElement.scrollHeight;
    }
    scrollHeight = (bodyScrollHeight - documentScrollHeight > 0) ? bodyScrollHeight : documentScrollHeight;
    return scrollHeight;
}
//浏览器视口的高度
function getWindowHeight() {
    　　var windowHeight = 0;
    　　if (document.compatMode == "CSS1Compat") {
        　　　　windowHeight = document.documentElement.clientHeight;
    　　} else {
        　　　　windowHeight = document.body.clientHeight;
    　　}
    　　return windowHeight;
}